Combustion gas purifier and internal combustion engine

ABSTRACT

A small capacity pre-catalytic system ( 34 ) is disposed immediately downstream of an exhaust port ( 18 ), and a large capacity main catalytic system ( 35 ) is disposed immediately downstream of the pre-catalytic system ( 34 ). The pre-catalytic system ( 34 ) includes finely divided catalyst supports ( 48 ), and a third stage heat exchanger (H 3 ) is disposed between these catalyst supports ( 48 ) so that a heat transfer tube ( 49 ) is bent in a zigzag manner. Fourth stage and fifth stage heat exchangers (H 4 , H 5 ) are disposed on the upstream side, in the flow of the exhaust gas, of the pre-catalytic system ( 34 ), and first and second stage heat exchangers (H 1 , H 2 ) are disposed on the downstream side, in the flow of the exhaust gas, of the main catalytic system ( 35 ). Water is made to flow through the first stage heat exchanger (H 1 ) to the fifth heat exchanger (H 5 ) in a direction opposite to that in which the exhaust gas flows, thereby exchanging heat with the exhaust gas. This allows the catalyst temperature to be actively controlled within the optimal temperature range without degrading the energy efficiency of the entire system.

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/JP01/00347 which has an Internationalfiling date of Jan. 19, 2001, which designated the United States ofAmerica.

FIELD OF THE INVENTION

The present invention relates to a combustion gas purification systemthat purifies, by an oxidation-reduction reaction, harmful components inthe combustion gas from a combustion system. Furthermore, the presentinvention relates to an internal combustion engine that is provided inan exhaust passage thereof with an exhaust gas purification system thatpurifies the exhaust gas, and a heat exchanger that exchanges heat withthe exhaust gas.

BACKGROUND ART

A catalytic system that purifies, by a catalytic reaction, harmfulcomponents in the exhaust gas from an internal combustion engine has astructure in which, for example, a platinum system catalyst is supportedon a catalyst support, and the catalyst has an optimal temperature forthe catalytic reaction. For example, when the catalyst temperature isbelow the activation temperature and the reactivity is poor, thecatalytic system is placed on the upstream side of the exhaust passagewhere the exhaust gas temperature is high and is thereby heated, or amethod is employed in which the catalytic system is heated by anelectric heater or the combustion gas generated in a combustion systemused exclusively for heating, so as to activate the catalytic reaction.Conversely, when the catalyst temperature becomes higher than its heatresistant temperature, enriching the air/fuel ratio relative to thetheoretical air/fuel ratio cools the catalyst by means of the heat ofvaporization of surplus fuel, thereby preventing degradation of thecatalyst.

Moreover, an arrangement is known from Japanese Patent ApplicationLaid-open No. 60-93110 in which heat exchangers are placed on both theupstream and downstream sides of a catalytic system disposed in anexhaust passage, and the catalyst is maintained at an appropriatetemperature by controlling the temperature of the exhaust gas.

In order to allow the catalytic system to function most efficiently, itis of course important to use it within a temperature range that isoptimal for the catalytic reaction, but if the catalyst temperaturedeviates from the temperature that is optimal for the catalyticreaction, it is also important that the catalyst temperature quicklyrecovers so that it is within the temperature range that is optimal forthe catalytic reaction (ref. Table 1). With regard to the deviation fromthe temperature that is optimal for the catalytic reaction referred tohere, there is a case in which the catalyst temperature is lower thanthe optimal temperature and a case in which it is higher, and forrecovering the catalyst temperature so that it is within the temperaturerange that is optimal for the catalytic reaction, there is a case wherethe catalyst temperature is increased and a case where it is decreased.

TABLE 1 Examples of temperature range of catalytic reaction Operationalmode of Generally used limit combustion system temperature ofpurification catalyst (application) Upper limit (° C.) Lower limit (°C.) Variable output/non- 800 to 900 250 to 300 rated operation (movabledevices such as automobiles) Constant output/rated 500 to 600 100 to 200operation (stationary plant machinery)

For example, immediately after an internal combustion engine starts, thetemperature of the catalytic system itself is close to ambient, and itis therefore necessary to heat the catalytic system as quickly aspossible so as to increase the catalyst temperature above the activationtemperature.

Among the conventional methods, the method in which the catalytic systemis placed in an upstream position of the exhaust passage where theexhaust gas temperature is high places a mechanical limit on how closethe catalytic system can be to the upstream end of the exhaust passagebecause of structural restrictions imposed by a system employing thecatalytic system or by the entire system. Furthermore, the method inwhich the catalytic system at low temperature is heated by an electricheater or combustion gas generated by a combustion system usedexclusively for heating requires a special energy source, and there isthe problem that the fuel consumption of the entire system increases.

Conversely, since an excessively high catalyst temperature causesdegradation of the catalyst, it is necessary to quickly cool thecatalyst temperature below the heat resistant temperature. In this case,since the air/fuel ratio is enriched to cool the catalyst by means ofthe heat of vaporization of surplus fuel, there is the problem of anincrease in the fuel consumption.

It should be noted here that in the arrangement described in JapanesePatent Application Laid-open No. 60-93110, it is inherently difficult toactively control the catalyst temperature. That is, in this method, aheat exchanger is disposed on the upstream side of the catalytic system,and there is extra thermal capacity within an exhaust passage throughwhich the exhaust gas, which is a heat source, passes. In other words,when the temperature of the main body of an internal combustion engineis still low immediately after a cold start, the heat of the exhaust gasis consumed by increasing the temperature of the heat exchanger that isfurther upstream than the catalytic system, and the temperature of theexhaust gas decreases before it increases the temperature of thecatalytic system.

Furthermore, when the catalyst is in an over-heated state, heat exchangeis first carried out between a low temperature medium and the exhaustgas within the heat exchanger on the upstream side of the catalyticsystem so as to decrease the temperature of the exhaust gas, and theexhaust gas whose temperature has been decreased by the heat exchange isthen supplied to the catalytic system, thereby indirectly suppressingany increase in the temperature of the catalyst. Of course, the heatexchanger on the downstream side of the catalytic system contributesalmost nothing to decreasing the catalyst temperature.

As hereinbefore described, since this method indirectly controls thethermal energy that is transferred to the catalyst by controlling thetemperature of the exhaust gas, which is a heat source, appropriatecontrol of the catalyst temperature is difficult.

Furthermore, an internal combustion engine that is equipped with anexhaust gas purification system in its exhaust passage is known fromJapanese Patent Application Laid-open Nos. 60-93110 and 8-68318, whereinheat exchangers are disposed in the exhaust passage on both the upstreamside and the downstream side of the exhaust gas purification system inan attempt to achieve both temperature control capability for theexhaust gas purification system and waste heat recovery capability forthe heat exchangers.

Although the exhaust gas purification system generates heat of reactionwhen removing harmful components from the exhaust gas, since in theabove-mentioned conventional arrangement, the exhaust gas purificationsystem and the heat exchangers are not in direct contact, it isdifficult to utilize effectively the heat of reaction generated by theexhaust gas purification system in the heat exchangers. Although it ispossible to activate the catalyst and protect it from being overheatedby controlling the temperature of the exhaust gas purification system bymeans of the flow rate of an operating medium flowing through the heatexchanger, in the above-mentioned conventional arrangement, since theexhaust gas purification system and the heat exchangers are not indirect contact with each other, it is difficult to control thetemperature of the exhaust gas purification system effectively.

DISCLOSURE OF THE INVENTION

The present invention has been carried out in view of theabove-mentioned circumstances, and it is a first object of the presentinvention to provide an exhaust gas purification system that canactively control the catalyst temperature in the optimal temperaturerange without degrading the energy efficiency of the entire system.

Furthermore, it is a second object of the present invention to enablethe best possible performance to be delivered by an exhaust gaspurification system and a heat exchanger provided in an exhaust passageof an internal combustion engine.

In order to accomplish the first object, in accordance with the presentinvention, there is proposed a combustion gas purification systemwherein a catalytic system that purifies a combustion gas is disposed inan exhaust passage guiding the combustion gas from a combustion system,and at least one part of the catalytic system is provided withtemperature adjustment means for adjusting the temperature thereof.

In accordance with this arrangement, since at least one part of thecatalytic system provided in the exhaust passage guiding the combustiongas from the combustion system is provided with the temperatureadjustment means for adjusting the temperature thereof, the temperatureof the catalytic system can be controlled actively by the temperatureadjustment means rather than passively via the temperature of thecombustion gas, and the catalyst temperature can thereby be controlledappropriately in the optimal temperature range.

Moreover, in addition to this arrangement, there is proposed acombustion gas purification system wherein the temperature adjustmentmeans is a heat exchanger.

In accordance with this arrangement, since the temperature adjustmentmeans for adjusting the temperature of the catalytic system is a heatexchanger, the thermal energy of the combustion gas and the thermalenergy generated by the catalytic reaction can be recovered effectively,thereby enhancing the performance of the heat exchanger.

Furthermore, in addition to this arrangement, there is proposed acombustion gas purification system wherein the catalytic system providedwith the temperature adjustment means is positioned on the upstream sideof the exhaust passage.

In accordance with this arrangement, since the catalytic system providedwith the temperature adjustment means is positioned on the upstream sideof the exhaust passage, after starting the combustion system thecatalytic system can be quickly heated above the catalyst activationtemperature using high temperature combustion gas without providing aspecial thermal energy source.

Moreover, in addition to this arrangement, there is proposed acombustion gas purification system wherein the temperature adjustmentmeans also controls the temperature of a part of the catalytic systemother than the one part of the catalytic system. In accordance with thisarrangement, since the temperature adjustment means for the one part ofthe catalytic system controls the temperature of the other part of thecatalytic system, the catalyst temperature of the entire catalyticsystem can be controlled appropriately within the optimal temperaturerange.

Furthermore, in addition to this arrangement, there is proposed acombustion gas purification system wherein temperature adjustment meansfor adjusting the temperature of the combustion gas is provided in theexhaust passage on the upstream side of the catalytic system.

In accordance with this arrangement, since the temperature adjustmentmeans is provided in the exhaust passage on the upstream side of thecatalytic system, the temperature of high temperature combustion gas canbe adjusted by the temperature adjustment means, thereby preventing thetemperature of the catalytic system from exceeding the heat resistanttemperature thereof.

Moreover, in addition to this arrangement, there is proposed acombustion gas purification system wherein the temperature adjustmentmeans is a heat exchanger.

In accordance with this arrangement, since the temperature adjustmentmeans provided in the exhaust passage on the upstream side of thecatalytic system is a heat exchanger, the thermal energy of hightemperature combustion gas can be recovered effectively, therebyenhancing the performance of the heat exchanger.

Furthermore, in addition to this arrangement, there is proposed acombustion gas purification system wherein at least the one part of thecatalytic system and the temperature adjustment means are disposed incontact so as to be able to exchange heat with each other.

In accordance with this arrangement, since the catalytic system providedin the exhaust passage of the internal combustion engine makes contactwith the temperature adjustment means so that they can exchange heatwith each other, control of the temperature of the catalytic system canbe carried out effectively by the temperature adjustment means, therebyactivating and protecting the catalyst.

Moreover, in addition to this arrangement, there is proposed acombustion gas purification system wherein at least the one part of thecatalytic system is formed from a metal and is integrated with thetemperature adjustment means at a contact site.

In accordance with this arrangement, since the catalytic system formedfrom a metal is integrated with the temperature adjustment means, heatexchange between the catalytic system and the temperature adjustmentmeans can be carried out extremely efficiently.

In the above-mentioned first to eighth aspects, an internal combustionengine 1 of an embodiment corresponds to the combustion system, apre-catalytic system 34 and a main catalytic system 35 of the embodimentcorrespond to the catalytic system, and a third stage heat exchanger H3,a fourth stage heat exchanger H4, and a fifth stage heat exchanger H5 ofthe embodiment correspond to the temperature adjustment means.

Furthermore, in order to accomplish the second object, in accordancewith the present invention, there is proposed an internal combustionengine including in an exhaust passage an exhaust gas purificationsystem that purifies the exhaust gas and a heat exchanger that exchangesheat with the exhaust gas, characterized in that at least one part ofthe exhaust gas purification system and at least one part of the heatexchanger are disposed in contact so as to be able to exchange heat witheach other.

In accordance with this arrangement, since the exhaust gas purificationsystem and the heat exchanger provided in the exhaust passage of theinternal combustion engine are disposed in contact so that they canexchange heat with each other, not only can the heat of reactiongenerated by the exhaust gas purification system removing harmfulcomponents from the exhaust gas be recovered effectively by the heatexchanger, thereby maximizing the waste heat recovery capability, butalso the temperature of the exhaust gas purification system can becontrolled effectively by the flow rate of an operating medium flowingthrough the heat exchanger, thereby activating and protecting thecatalyst.

Moreover, in addition to this arrangement, there is proposed an internalcombustion engine wherein stirring means for stirring the flow ofexhaust gas is provided on the upstream side of the section where theexhaust gas purification system and the heat exchanger are in contact.

In accordance with this arrangement, since the stirring means isprovided on the upstream side of the section where the exhaust gaspurification system and the heat exchanger are in contact, the flow ofexhaust gas is stirred and the exhaust gas can be contacted with theexhaust gas purification system and the heat exchanger uniformly andsufficiently, thereby further enhancing the exhaust gas purifying effectand the heat exchange effect.

Furthermore, in addition to this arrangement, there is proposed aninternal combustion engine wherein at least the one part of the exhaustgas purification system is formed from a metal and is integrated with atleast the one part of the heat exchanger at the contact site.

In accordance with this arrangement, since the exhaust gas purificationsystem formed from a metal is integrated with the heat exchanger, heatexchange between the exhaust gas purification system and the heatexchanger can be carried out extremely efficiently.

In the above-mentioned ninth to eleventh aspects, a first stage metalcatalytic system 246A to a fourth stage metal catalytic system 246D ofan embodiment correspond to the exhaust gas purification system, a firststage heat exchanger H1 to a fifth stage heat exchanger H5 of theembodiment corresponds to the heat exchanger, and the stirring meanscorresponds to a guide vane 245 of the embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 18 illustrate a first embodiment of the present invention;FIG. 1 is a diagram showing the overall arrangement of a drive systememploying the Rankine cycle; FIG. 2 is a diagram showing the structureof a power transmission system of the drive system; FIG. 3 is alongitudinal cross section of a cylinder head part of an internalcombustion engine; FIG. 4 is a cross section along line 4—4 in FIG. 3;FIG. 5 is a magnified cross section of an essential part in FIG. 3; FIG.6 is a cross section along line 6—6 in FIG. 5; FIG. 7 is a magnifiedview of an essential part in FIG. 5; FIG. 8 is a magnified view of anessential part in FIG. 6; FIG. 9A is a diagram showing a heat transfertube of a fourth stage heat exchanger; FIG. 9B is a view from arrow b inFIG. 9A; FIG. 9C is a view from arrow c in FIG. 9A; FIG. 10 is anexploded perspective view of a pre-catalytic system; FIG. 11 is aschematic diagram showing a water supply route of an evaporator; FIG. 12is an exploded perspective view of the evaporator; FIG. 13 is a diagramshowing the layout of catalytic systems and heat exchangers in anembodiment and comparative embodiments; FIG. 14 is a graph showing therelationship between the exhaust gas temperature and the distance froman exhaust port when cold starting; FIG. 15 is a graph showing therelationship between the exhaust gas temperature and the distance fromthe exhaust port at high temperature; FIG. 16 is a graph explaining theeffect of multiple water supplies; FIG. 17 is a graph showing therelationship between the Reynolds number and the heat transferperformance for steady flow and pulsed flow; and FIG. 18 is a graphshowing the relationship between the Reynolds number and the heattransfer performance at different exhaust pressures.

FIGS. 19 to 29 illustrate a second embodiment of the present invention;FIG. 19 is a longitudinal cross section of a cylinder head part of aninternal combustion engine; FIG. 20 is a cross section of an essentialpart in FIG. 19; FIG. 21 is a view from the arrowed line 21—21 in FIG.20; FIG. 22 is a cross section along line 22—22 in FIG. 20; FIG. 23 is across section along line 23—23 in FIG. 20; FIG. 24 is a magnified viewof an essential part in FIG. 20; FIG. 25 is a magnified view of part 25in FIG. 22; FIG. 26 is a cross section along line 26—26 in FIG. 21; FIG.27A is a diagram showing a heat transfer tube of a fourth stage heatexchanger; FIG. 27B is a view from arrow b in FIG. 27A; FIG. 27C is aview from arrow c in FIG. 27A; FIG. 28 is an exploded perspective viewof a metal catalytic system and a third stage heat exchanger; and FIG.29 is a schematic view showing a water supply route of an evaporator.

BEST MODE FOR CARRYING OUT THE INVENTION

The first embodiment of the present invention is explained below byreference to FIGS. 1 to 18.

In FIG. 1, a waste heat recovery system 2 for an internal combustionengine 1, as a combustion system mounted in an automobile, includes anevaporator 3 that generates vapor having increased temperature andpressure, that is, high-pressure vapor, using, as a heat source, wasteheat such as, for example, exhaust gas from the internal combustionengine 1; an expander 4 that generates a shaft output by expansion ofthe high-pressure vapor; a condenser 5 that liquefies the vapor havingdecreased temperature and pressure, that is, low-pressure vapor,discharged from the expander 4 after the expansion; and a water supplypump 6 that supplies water from the condenser 5 to the evaporator 3.

As is clear by referring also to FIG. 2, a power transmission system 121connected to the waste heat recovery system 2 includes a planetary gearmechanism 122, a belt type continuously variable transmission 123, andan electric generator/motor 124.

The planetary gear mechanism 122 includes a sun gear 125, a ring gear126, a planetary carrier 127, and a plurality of planetary gears 128axially supported by the planetary carrier 127 and meshingsimultaneously with the sun gear 125 and the ring gear 126. Theplanetary carrier 127 connected to an output shaft 129 of the expander 4can engage with a casing, which is not illustrated, via a carrier brake130. The sun gear 125 connected to an input/output shaft 131 of theelectric generator/motor 124 can engage with the casing, which is notillustrated, via a sun gear brake 132. The ring gear 126 can engage withthe casing, which is not illustrated, via a ring gear brake 133. Each ofthe carrier brake 130, the sun gear brake 132, and the ring gear brake133 is formed from a hydraulic brake or an electromagnetic brake.

The electric generator/motor 124 is connected to a battery 134 that canbe charged and discharged. The electric generator/motor 124 charges thebattery 134 when it is driven by the shaft output of the expander 4 orthe internal combustion engine 1 so as to function as an electricgenerator, and it assists the drive by the internal combustion engine 1of driven wheels or starts the internal combustion engine 1 when itfunctions as a motor powered by the battery 134.

The belt type continuously variable transmission 123 includes a drivepulley 136 provided on an input shaft 135, a follower pulley 138provided on an output shaft 137, and an endless belt 139 wrapped aroundthe two pulleys 136, 138. The groove width of the drive pulley 136 andthe groove width of the follower pulley 138 are individually variable byhydraulic control or electric control; increasing the groove width ofthe drive pulley 136 and decreasing the groove width of the followerpulley 138 continuously change the gear ratio to the LOW side, anddecreasing the groove width of the drive pulley 136 and increasing thegroove width of the follower pulley 138 continuously changes the gearratio to the TOP side.

A drive gear 140 provided on the ring gear 126 of the planetary gearmechanism 122 meshes with a driven gear 141 provided on the input shaft135 of the belt type continuously variable transmission 123. The shaftoutput of the internal combustion engine 1 is transmitted to atransmission 143 via an output shaft 142, and the output from thetransmission 143 is transmitted to driven wheels, which are notillustrated. A drive gear 144 provided on the output shaft 137 of thebelt type continuously variable transmission 123 meshes with a drivengear 145 provided on the output shaft 142 of the internal combustionengine 1.

Torque limiters 146, 147 are provided on the output shaft 129 of theexpander 4 and the input/output shaft 131 of the electricgenerator/motor 124 respectively. The torque limiters 146, 147 slip whena torque equal to or greater than a predetermined value is applied tothe expander 4 or the electric generator/motor 124, thereby preventingan excess load being generated. The torque limiters 146, 147 can bereplaced with clutches that disengage when an overload torque that isequal to or greater than a predetermined value is generated. A clutch148 is provided on the output shaft 137 of the belt type continuouslyvariable transmission 123. The clutch 148 is for preventing an overloadfrom being applied to the expander 4 due to the driving forcetransmitted back from the internal combustion engine 1 or the drivenwheels, and it provides a connection between the internal combustionengine 1 and the expander 4 when it is engaged, and disconnects theinternal combustion engine 1 from the expander 4 when it is disengaged.

When the sun gear 125 is fixed by engaging the sun gear brake 132 of theplanetary gear mechanism 122, each of the planetary carrier 127 and thering gear 126 becomes an input element or an output element; a drivingforce input from the expander 4 into the planetary carrier 127 is outputto the ring gear 126 and is then transmitted therefrom to the outputshaft 142 of the internal combustion engine 1 via the drive gear 140,the driven gear 141, the belt type continuously variable transmission123, the drive gear 144, and the driven gear 145, and the shaft outputof the expander 4 can thereby assist the shaft output of the internalcombustion engine 1. On the other hand, if a driving force istransmitted via the reverse of the above route when starting theexpander 4, the shaft output of the internal combustion engine 1 cansmoothly start the expander 4.

When the ring gear 126 is fixed by engaging the ring gear brake 133 ofthe planetary gear mechanism 122, each of the expander 4 or the electricgenerator/motor 124 becomes an input element and an output element; adriving force input from the expander 4 into the planetary carrier 127is output to the electric generator/motor 124 via the sun gear 125, thusallowing the electric generator/motor 124 to function as an electricgenerator, and thereby charging the battery 134. On the other hand, if adriving force is transmitted via the reverse of the above route whenstarting the expander 4, the shaft output of the electricgenerator/motor 124 functioning as a motor can smoothly start theexpander 4.

When the planetary carrier 127 is fixed by engaging the carrier brake130 of the planetary gear mechanism 122, each of the sun gear 125 andthe ring gear 126 becomes an input element or an output element. Adriving force input into the sun gear 125 from the electricgenerator/motor 124 functioning as a motor is therefore output from thering gear 126, is transmitted therefrom to the output shaft 142 of theinternal combustion engine 1 via the drive gear 140, the driven gear141, the belt type continuously variable transmission 123, the drivegear 144, and the driven gear 145, and assists the shaft output of theinternal combustion engine 1 or starts the internal combustion engine 1.On the other hand, transmitting the shaft output of the internalcombustion engine 1 to the electric generator/motor 124 via the reverseof the above route allows the electric generator/motor 124 to functionas an electric generator, thereby charging the battery 134.

The structure of the evaporator 3 of the waste heat recovery system 2for the internal combustion engine 1 is now explained in detail byreference to FIGS. 3 to 12.

As shown in FIGS. 3 to 8, the in-line three cylinder internal combustionengine 1 includes a cylinder block 11, a cylinder head 12, and a headcover 13, which are laminated one on another, and pistons 15 areslidably fitted in three cylinder bores 14 formed in the cylinder block11. Among intake ports 17 and exhaust ports 18 communicating with threecorresponding combustion chambers 16 formed in the cylinder head 12, theintake ports 17 are bored within the cylinder head 12 as isconventional, but the exhaust ports 18 are formed from a separate memberand joined to the cylinder head 12.

The upper end of a stem 21 of an intake valve 20 that opens and closesan intake valve hole 19 abuts against one end of an intake rocker arm 23pivotably supported on an intake rocker arm shaft 22, and the upper endof a stem 26 of an exhaust valve 25 that opens and closes an exhaustvalve hole 24 abuts against one end of an exhaust rocker arm 28pivotably supported on an exhaust rocker arm shaft 27. The other end ofthe intake rocker arm 23 and the other end of the exhaust rocker arm 28abut against an intake cam 30 and an exhaust cam 31 respectivelyprovided on a camshaft 29 rotating in association with a crankshaft,which is not illustrated, thereby making the intake valve 20 and theexhaust valve 25 open and close.

Provided on the side face of the cylinder head 12 on the exhaust side isthe evaporator 3 that generates vapor having increased temperature andpressure, that is, high-pressure vapor, using the exhaust gas of theinternal combustion engine 1 as a heat source. The evaporator 3 includesan exhaust passage 33 having the three exhaust ports 18 as the base endand extending to an exhaust pipe 32, three pre-catalytic systems 34 andthree main catalytic systems 35 disposed within the exhaust passage 33,and heat exchangers H1 to H5 carrying out heat exchange with the exhaustgas flowing in the exhaust passage 33.

Each of the exhaust ports 18 is formed from a uniform diameter part 18 apositioned on the upstream side of the flow of the exhaust gas, andhaving a substantially constant diameter, and an increasing diameterpart 18 b provided so as to be connected to the downstream side of theuniform diameter part 18 a and having a diameter that increases in atrumpet shape; the fifth stage heat exchanger H5 is provided around theouter periphery of the uniform diameter part 18 a, and the fourth stageheat exchanger H4 is provided within the increasing diameter part 18 b.The fifth stage heat exchanger H5 is formed from about 5 turns of asingle heat transfer tube 37 wound around the outer periphery of theuniform diameter part 18 a. The fourth stage heat exchanger H4 is formedfrom multiple windings of a single heat transfer tube 38 that is housedwithin the increasing diameter part 18 b, and the heat transfer tube 37of the fifth stage heat exchanger H5 runs through an opening (notillustrated) formed in the exhaust port 18 and is continuous to the heattransfer tube 38 of the fourth stage heat exchanger H4.

As is clear from reference to FIGS. 9A to 9C, the heat transfer tube 38of the fourth stage heat exchanger H4 is wound in a triple coil shapethat is tapered so as to follow the shape of the interior of theincreasing diameter part 18 b of the exhaust port 18; the coil in theinner layer is wound from the rear (the left-hand side in the figure)toward the front (the right-hand side in the figure) while decreasing indiameter and is folded back at the front end; this is followed by thecoil in the middle layer, which is wound from the front toward the rearwhile increasing in diameter and is folded back at the rear end; andthis is followed by the coil in the outer layer, which is wound from therear toward the front while decreasing in diameter. A water inlet shownin FIG. 9B is connected to the third stage heat exchanger H3, which ison the upstream side and will be described later, and a water outletshown in FIG. 9C is connected to the heat transfer tube 37 of the fifthstage heat exchanger H5, which is on the downstream side. The circlednumerals to shown in FIG. 9A show the route via which water flowsthrough the heat transfer tube 38.

In addition, winding the heat transfer tube 38 of the fourth stage heatexchanger H4 in the triple coil shape that is tapered so as to followthe shape of the interior of the increasing diameter part 18 b of theexhaust port 18 makes it possible to have a rectifying effect on theexhaust gas that flows through the increasing diameter part 18 b,thereby contributing to a reduction in the circulation resistance.

As is most clearly shown in FIGS. 7 and 8, an annular distributionpassage forming member 41 is integrally formed on the rear end of theincreasing diameter part 18 b of the exhaust port 18, and by joining aseparate annular distribution passage forming member 42 to the rear faceof the distribution passage forming member 41, a third circulardistribution passage 43 is formed between the two distribution passageforming members 41, 42. The upstream end of the heat transfer tube 38 ofthe fourth stage heat exchanger H4 is connected to the third circulardistribution passage 43.

The front end of a cylindrical case 44 covering the outer periphery ofthe pre-catalytic system 34 is joined to the distribution passageforming member 42, and a second circular distribution passage 47 isformed between two annular distribution passage forming members 45, 46,which are superimposed one on another and joined to the rear end of thecylindrical case 44. The pre-catalytic system 34 and the third stageheat exchanger H3 are disposed within the cylindrical case 44.

The pre-catalytic system 34 includes seven sheets of catalyst support 48formed in honeycomb plates from a metal, on the surface of which issupported a known exhaust gas purification catalyst. The third stageheat exchanger H3, which is disposed within the cylindrical case 44 soas to surround the seven sheets of catalyst support 48, is formed fromtwo bent heat transfer tubes 49, 49 (see FIG. 10). Each of the heattransfer tubes 49, 49 is bent in a zigzag within a circular plane, thenmoves to the next plane that is separated therefrom by one pitch in theaxial direction and is bent in the same zigzag shape, this beingrepeated to give a cylindrical outer shape having a plurality ofpitches. The seven sheets of catalyst support 48 are housed within theinternal space formed by interlacing together the two heat transfertubes 49, 49. Here, the two heat transfer tubes 49, 49 are integrated soas to be in intimate contact with the surface of the seven sheets ofcatalyst support 48. The upstream ends of the two heat transfer tubes49, 49 are connected to the second circular distribution passage 47formed between the distribution passage forming members 45, 46, and thedownstream ends thereof are connected to the third circular distributionpassage 43 formed between the distribution passage forming members 41,42.

Two cylindrical cases 50, 51 are coaxially disposed outside, in theradial direction of the cylindrical case 44 of the pre-catalytic system34, and the second stage heat exchanger H2 is disposed in an annularform between the two cylindrical cases 50, 51. The second stage heatexchanger H2 is formed from a large number of heat transfer tubes 52wound in a coiled shape in one direction and a large number of heattransfer tubes 53 wound in a coiled shape in the other direction, thetubes 52, 53 being disposed alternately so that parts thereof are meshedtogether, thereby increasing the placement density of the heat transfertubes 52, 53 within the space. The outer periphery of the pre-catalyticsystem 34 is thus surrounded by the heat transfer tubes 52, 53.

A first circular distribution passage 56 is formed between adistribution passage forming member 54 fixed to the front end of thecylindrical case 50 on the outer side and a distribution passage formingmember 55 joined to the front face of the distribution passage formingmember 54. The upstream ends of the heat transfer tubes 52, 53 areconnected to the first circular distribution passage 56, and thedownstream ends of the heat transfer tubes 52, 53 are connected to thesecond circular distribution passage 47.

The three pre-catalytic systems 34 are combined into one by apress-formed metal plate mounting plate 57 and fixed to the cylinderhead 12. Three openings 57 a are formed in the mounting plate 57, andthe distribution passage forming member 41 of each of the increasingdiameter parts 18 b of the three exhaust ports 18 is integrally fixed tothe corresponding opening 57 a. An oval-shaped flange 58 fixed to theouter periphery of the mounting plate 57 is fixed to the cylinder head12 by sixteen bolts 59.

The three main catalytic systems 35 are disposed to the rear of thethree pre-catalytic systems 34. The main catalytic systems 35 are formedby supporting a catalyst on the surface of catalyst supports 60 having ahoneycomb structure formed in an overall cylindrical shape, and thickring members 61 are fitted around the outer peripheries thereof. Themain catalytic systems 35 have a diameter larger than that of thepre-catalytic systems 34, and the main catalytic systems 35 are dividedinto inner layer parts 35 a having the same diameter as that of thepre-catalytic systems 34 and outer layer parts 35 b that project outsidethe outer peripheries of the pre-catalytic systems 34. In order to sealopposing parts of the pre-catalytic systems 34 and the main catalyticsystems 35, seal members 63 supported on the rear face of thedistribution passage forming member 46 via springs 62 resiliently abutagainst the front faces of the main catalytic systems 35. End caps 65are supported, via springs 64, on the rear ends of the ring members 61on the outer peripheries of the main catalytic systems 35. The rearfaces of the three end caps 65 abut against projections 66 a provided onthe front face of an inner wall member 66, which will be describedlater, and are pushed forward.

The outsides of the three pre-catalytic systems 34 and the three maincatalytic systems 35 are covered with a detachable common cover 71. Thecover 71 includes a plate-shaped distribution passage forming member 72having a mounting hole 72 a for the exhaust pipe 32 in its center and atriple ring-shaped distribution passage forming member 73 joined to thefront face of the distribution passage forming member 72, and a firsttriple ring-shaped distribution passage 74 is formed between the twodistribution passage forming members 72, 73. A tubular member 75positioned radially outside and a tubular member 76 positioned radiallyinside extend forward, with a slight gap therebetween, from the triplering-shaped distribution passage forming member 73, and an oval flange77 provided on the front end of the outer tubular member 75 issuperimposed on the flange 58 and they are tightened together by thebolts 59.

A triple ring-shaped distribution passage forming member 78 is fixed tothe front end of the inner tubular member 76, and a second triplering-shaped distribution passage 80 is formed by joining, to the frontface of the distribution passage forming member 78, a distributionpassage forming member 79 of the substantially same shape. The firsttriple ring-shaped distribution passage 74 and the second triplering-shaped distribution passage 80 have an identical shape and faceeach other in the front to rear direction. The cup-shaped inner wallmember 66 is housed within the cover 71, and the first stage heatexchanger H1 is disposed between the outer periphery of the inner wallmember 66 and the inner periphery of the inner tubular member 76.

The first stage heat exchanger H1 has a similar structure to that of thesecond stage heat exchangers H2; a large number of heat transfer tubes81 wound in a coiled shape in one direction and a large number of heattransfer tubes 82 wound in a coiled shape in the other direction aredisposed alternately so that parts thereof are meshed together, andthese heat transfer tubes 81, 82 surround the outer peripheries of thesecond stage heat exchangers H2 and the outer peripheries of the maincatalytic systems 35. The upstream ends of the heat transfer tubes 81,82 are connected to the first triple ring-shaped distribution passage74, and the downstream ends thereof are connected to the second triplering-shaped distribution passage 80.

The materials for the heat transfer tubes 37 of the fifth stage heatexchangers H5, the heat transfer tubes 38 of the fourth stage heatexchangers H4, the heat transfer tubes 49 of the third stage heatexchangers H3, the heat transfer tubes 52, 53 of the second stage heatexchangers H2, and the heat transfer tubes 81, 82 of the first stageheat exchanger H1 are preferably heat-resistant stainless steel(austenite type such as SUS 316L or SUS 310S, ferrite type such as SUS430 or SUS 444) or a nickel-based heat-resistant alloy. Joining of theheat transfer tubes is preferably carried out by brazing or mechanicalrestraint.

Furthermore, with regard to the catalyst supports 48 for thepre-catalytic systems 34, heat-resistant stainless steel (e.g., 20% byweight Cr-5% by weight Al ferrite type stainless steel) or anickel-based heat-resistant alloy foil (thickness 0.1 mm or below) ispreferable, and with regard to the catalyst supports 60 for the maincatalytic systems 35, cordylite is preferable.

As is clear from reference to FIG. 11, a water inlet 83, into whichwater that is a source of high pressure vapor is supplied, is providedin a central part of the first triple ring-shaped distribution passage74, which communicates with the second triple ring-shaped distributionpassage 80 via a large number of the heat transfer tubes 81, 82 of thefirst stage heat exchanger H1 disposed so as to surround the outerperipheries of the three main catalytic systems 35, and the secondtriple ring-shaped distribution passage 80 communicates with the threefirst circular distribution passages 56 via two detachable couplings 84.

The three first circular distribution passages 56 communicate with thethree second circular distribution passages 47 via the heat transfertubes 52, 53 of the second stage heat exchangers H2 disposed so as tosurround the outer peripheries of the three pre-catalytic systems 34,and each of these three second circular distribution passages 47communicates with the corresponding one of the three third circulardistribution passages 43 via two of the heat transfer tubes 49 of thethird stage heat exchangers H3 disposed within the three pre-catalyticsystems 34. Each of the three third circular distribution passages 43continues through one of the heat transfer tubes 38 of the fourth stageheat exchangers H4 that pass through the interiors of the three exhaustports 18 and one of the heat transfer tubes 37 of the fifth stage heatexchangers H5 that pass around the exteriors of the three exhaust ports18, and they are then combined together by a coupling 85 and supplied tothe expander 4 in a subsequent stage from a water outlet 86.

Water that has been supplied from a midstream water inlet 87 branches inthree directions in a distributor 88, a part thereof is suppliedmidstream to the three first circular distribution passages 56 via thecouplings 84, a part thereof is supplied midstream to the three secondcircular distribution passages 47, and a part thereof is suppliedmidstream to the three third circular distribution passages 43.

In this way, while the water that is supplied from the water inlet 83travels to the water outlet 86 via the first stage heat exchanger H1→thesecond stage heat exchangers H2→the third stage heat exchangers H3→thefourth stage heat exchangers H4→the fifth stage heat exchangers H5, itexchanges heat with exhaust gas that comes out of the internalcombustion engine 1 and flows in a direction opposite to that in whichthe water flows, the water becoming vapor.

That is, while passing through the uniform diameter parts 18 a of thethree exhaust ports 18, the exhaust gas coming out of the internalcombustion engine 1 exchanges heat with the fifth stage heat exchangersH5 formed from the heat transfer tubes 37 wound around the outerperipheries of the uniform diameter parts 18 a. The exhaust gas that hasflowed from the uniform diameter parts 18 a of the exhaust ports 18 intothe increasing diameter parts 18 b exchanges heat by direct contact withthe fourth stage heat exchangers H4 formed from the heat transfer tubes38 wound in a triple coil shape and housed within the increasingdiameter parts 18 b. The exhaust gas passes from the exhaust ports 18through the interior of the seven catalyst supports 48 of each of thethree pre-catalytic systems 34 to purify its harmful components and, atthis point, exchanges heat with the third stage heat exchangers H3formed from the heat transfer tubes 49 surrounding the peripheries ofthe catalyst supports 48.

The exhaust gas that has passed through the three pre-catalytic systems34 passes through the inner layer parts 35 a of the three main catalyticsystems 35 from the front to the rear, is then blocked by the end caps65 and makes a U-turn, and passes through the outer layer parts 35 b ofthe main catalytic systems 35 from the rear to the front; during thisstage, harmful components in the exhaust gas are purified by the maincatalytic systems 35. The exhaust gas coming out of the main catalyticsystems 35 exchanges heat while flowing, from the rear to the front,through the second stage heat exchangers H2 formed from the heattransfer tubes 52, 53 disposed between the pairs of cylindrical cases50, 51, then changes direction through 180°, exchanges heat whileflowing, from the front to the rear, through the first stage heatexchanger H1 formed from the heat transfer tubes 81, 82 disposed betweenthe tubular member 76 and the inner wall member 66, and is finallydischarged into the exhaust pipe 32 through the mounting hole 72 a ofthe distribution passage forming member 72.

The procedure for assembling the evaporator 3 having the above-mentionedstructure is explained mainly by reference to FIG. 12.

Firstly, mounted in the cylinder head 12 is a sub-assembly integrallyformed from the three exhaust ports 18, to which the fourth stage heatexchangers H4 and the fifth stage heat exchangers H5 are preassembled,and the three pre-catalytic systems 34, to which the second stage heatexchangers H2 and the third stage heat exchangers H3 are preassembled.That is, the distribution passage forming members 41 provided in thethree exhaust ports 18 are integrally fixed to the three openings 57 aof the plate-shaped mounting plate 57, and the oval-shaped flange 58fixed to the outer periphery of the mounting plate 57 is positioned onthe cylinder head 12.

Subsequently, the three main catalytic systems 35 are brought up to thethree pre-catalytic systems 34 from the rear, and the outer peripheriesat the front end of the ring members 61 on the outer peripheries of themain catalytic systems 35 are fitted to the outer peripheries at therear end of the cylindrical cases 50 of the second stage heat exchangersH2. At this point, the seal members 63 supported on the rear faces ofthe distribution passage forming members 46 via the springs 62resiliently abut against the front faces of the main catalytic systems35 (see FIG. 4).

Subsequently, the cover 71 is moved forward so as to cover the outerperipheries of the three main catalytic systems 35 and the three secondstage heat exchangers H2 with the triple ring-shaped first stage heatexchanger H1 in which three circles are staggered in the lateraldirection and superimposed one on another, and the flange 77 provided onthe tubular member 75 of the cover 71 is superimposed on the rear faceof the flange 58 of the mounting plate 57 and joined to the cylinderhead 12 by the sixteen bolts 59. At this point, the projections 66 a ofthe inner wall member 66 within the cover 71 push the end caps 65 of themain catalytic systems 35 forward so as to compress the springs 64between spring seats 67 provided on the outer peripheries of the endcaps 65 and spring seats 68 provided on the rear ends of the ringmembers 61 on the outer peripheries of the main catalytic systems 35(see FIG. 4).

As hereinbefore described, since the assembly is carried out so as togive a slight gap in the radial direction between an inner layer partincluding the pre-catalytic systems 34 and the main catalytic systems35, and the cover 71, which is an outer layer part covering the outerperipheries thereof, thermal expansion thereof in the radial directioncan be absorbed. Furthermore, since the main catalytic systems 35 areresiliently retained by the springs 62 and 64 between the rear faces ofthe pre-catalytic systems 34 and the front face of the inner wall member66 of the cover 71, thermal expansion of the pre-catalytic systems 34and the main catalytic systems 35 in the axial direction can beabsorbed.

Finally, the three first circular distribution passages 56 are eachconnected to the second triple ring-shaped distribution passage 80 atthe front end of the cover 71 via the couplings 84, and the three heattransfer tubes 37 of the fifth stage heat exchangers H5 extending fromthe three exhaust ports 18 are combined by the coupling 85 to therebycomplete the assembly of the evaporator 3.

It should be noted here that as shown in FIG. 13, in Present EmbodimentP-1, a catalytic system for purifying an exhaust gas is divided into thepre-catalytic systems 34 on the upstream side and the main catalyticsystems 35 on the downstream side, the fourth stage heat exchangers H4and the fifth stage heat exchangers H5 are disposed on the upstream sideof the flow of the exhaust gas, of the pre-catalytic systems 34, and thefirst stage heat exchanger H1 and the second stage heat exchangers H2are disposed on the downstream side of the flow of the exhaust gas, ofthe main catalytic systems 35. As hereinbefore described, the thirdstage heat exchangers H3 are housed within the pre-catalytic systems 34.

On the other hand, Comparative Example C-0 includes neither a catalyticsystem nor a heat exchanger, Comparative Example C-1 includes only amain catalytic system, Comparative Example C-2 includes a main catalyticsystem as the stage following a pre-catalytic system, and ComparativeExample C-3 includes heat exchangers as both the stage prior to and thestage following a main catalytic system.

FIG. 14 shows the change in temperature of the exhaust gas from theupstream side to the downstream side (L0→L1→L2→L3→L4→L5) during a coolperiod immediately after starting the internal combustion engine 1. Inaccordance with Present Embodiment P-1, since the pre-catalytic systems34 are disposed on the upstream side of the exhaust passage 33 and thecapacity of the pre-catalytic systems 34 is set small, the temperatureof the pre-catalytic systems 34 can be increased quickly to the catalystactivation temperature or above even during the cool period, therebyreducing the harmful components in the exhaust gas effectively.

Moreover, although the exhaust gas purification performance would beinsufficient with only the small capacity pre-catalytic systems 34,disposition of the main catalytic systems 35 having a large capacity onthe downstream side thereof can adequately compensate for the exhaustgas purification performance of the small capacity pre-catalytic systems34. Furthermore, since the direction of flow of the exhaust gas isinverted between the inner layer parts 35 a and the outer layer parts 35b of the main catalytic systems 35, when the exhaust gas passes firstlythrough the inner layer parts 35 a of the main catalytic systems 35, itstemperature increases due to the catalytic reaction, the exhaust gashaving increased temperature is supplied to the outer layer parts 35 bof the main catalytic systems 35, and when the exhaust gas turns aroundthrough 180°, harmful components in the exhaust gas are mixedeffectively thus promoting the catalytic reaction in the outer layerparts 35 b, and thereby enhancing the overall exhaust gas purificationperformance of the main catalytic systems 35. Moreover, the exhaust gasin the inner layer parts 35 a is covered by the exhaust gas in the outerlayer parts 35 b, thus preventing thermal leakage and thereby preventingany degradation in the heat exchange efficiency.

FIG. 15 shows the change in temperature of the exhaust gas from theupstream side to the downstream side when the internal combustion engine1 is being operated at high temperature. In accordance with the PresentEmbodiment P-1, although there is a possibility of degradation due toexposure to high temperature exhaust gas because the pre-catalyticsystems 34 are positioned close to the exhaust ports 18, since thefourth stage heat exchangers H4 and the fifth stage heat exchangers H5are placed in the exhaust ports 18, it is possible to prevent thecatalyst temperature of the pre-catalytic systems 34 from exceeding theheat resistant temperature. Furthermore, since, within the pre-catalyticsystems 34, the catalyst supports 48 of the third stage heat exchangersH3 are divided into seven narrow pieces, and the zigzag-bent heattransfer tubes 49 of the third stage heat exchangers H3 are in directcontact with the peripheries of the catalyst supports 48, the catalysttemperature of the pre-catalytic systems 34 can more reliably beprevented from exceeding the heat resistant temperature.

Moreover, since the first stage heat exchanger H1, the second stage heatexchangers H2, the third stage heat exchangers H3, the fourth stage heatexchangers H4, and the fifth stage heat exchangers H5 are connected inline, and water is supplied sequentially from the first stage heatexchanger H1 side to the fifth stage heat exchangers H5 side (this watersupply method is called one-way water supply), increasing/decreasing theamount of water supplied can appropriately control the temperatures ofthe pre-catalytic systems 34 and the main catalytic systems 35 accordingto the operational state of the internal combustion engine 1 (see Table2).

TABLE 2 Comparison of cold starting characteristics and high temperatureheat resistance High temperature heat Cold starting characteristicsresistance (early activation) (catalyst degradation) Overall evaluationComparative C-1 Poor Poor Poor Example C-2 Good Poor Poor C-3 Poor GoodPoor :Control of flow rate of low temperature medium : No :No in heatexchanger Embodiment P-1 Good Good Good :Control of flow rate of lowtemperature medium :Yes :Yes in heat exchanger (flow rate: low) (flowrate: high)

Furthermore, supplying water midstream at three positions in the watersupply route from the first stage heat exchanger H1 to the fifth stageheat exchangers H5, that is, the first circular distribution passages 56immediately upstream of the second stage heat exchangers H2, the secondcircular distribution passages 47 immediately upstream of the thirdstage heat exchangers H3, and the third circular distribution passages43 immediately upstream of the fourth stage heat exchangers H4, andindividually controlling the amount of water supplied to the secondstage to fourth stage heat exchangers H2, H3, H4 according to changes inthe operational state (the flow rate of the exhaust gas or thetemperature of the exhaust gas) of the internal combustion engine 1 andthe catalyst temperature (this water supply method is called multiplewater supply) can yet more finely control the catalyst temperature ofthe pre-catalytic systems 34 and the main catalytic systems 35 attemperatures appropriate for the catalytic reaction (see Table 3 andFIG. 16).

TABLE 3 Ability to track catalyst temperature when thermal loadfluctuates Operational status of combustion system (thermal load) Lowthermal load Medium thermal load High thermal load Purific- Purific-Purific- ation ation ation Flow rate Temp. Track- perform- Temp. Track-perform- Temp. Track- perform- control method State of catalyst rangeability ance range ability ance range ability ance One way waterPre-catalyst Good Rapid Good Good Rapid Good Good Rapid Good supply Maincatalyst Lower Slow Poor Lower Slow Poor Lower Slow Poor Midstream:Total amount of (None) (None) (None) water water supplied Small MediumLarge supply Multiple water Pre-catalyst Good Rapid Good Good Rapid GoodGood Rapid Good supply Main catalyst Good Rapid Good Good Rapid GoodGood Rapid Good Midstream (Position of (A) (B) (C) (A) (B) (C) (A) (B)(C) water midstream supply water supply) :Midstream water :Trace :Trace:Trace :Trace :Low :Low :Low :Medium :High supplied :total amount of:Small :Medium :Large water supplied

The effect of multiple water supply is further explained by reference toFIG. 16. When carrying out one way water supply, as shown by a brokenline, if the amount of water supplied is set small in line with a lowload state of the internal combustion engine 1, the catalyst temperaturepasses the lower limit temperature (catalyst activation temperature)earlier, but it also quickly goes beyond the upper limit temperature(catalyst heat resistant temperature). Conversely, if the amount ofwater supply is set large in line with a high load state of the internalcombustion engine 1, although the catalyst temperature passes the lowerlimit temperature (catalyst activation temperature) slowly, going beyondthe upper limit temperature (catalyst heat resistant temperature) can bedelayed. It is thus difficult to achieve both early activation anddurability of the catalyst with the one way water supply, but by settingthe amount of water supplied low when the internal combustion engine 1is in a low load state and increasing the amount of water supplied bymidstream water supply while the load is increasing, both earlyactivation and durability of the catalyst can be achieved.

The reason why the lines for the pre-catalytic systems 34 are on theleft side and the lines for the main catalytic systems 35 are on theright side in FIG. 16 is that the capacity of the pre-catalytic systems34 is small and the capacity of the main catalytic systems 35 is large.It is of course possible to control the temperatures of thepre-catalytic systems 34 and the main catalytic systems 35 yet morefinely by individually controlling the amounts of water supplied to themidstream water inlets at the three positions.

As hereinbefore described, in accordance with Present Embodiment P-1, incomparison with Comparative Examples C-0 to C-3, the overall exhaust gaspurification performance and durability of the catalytic system can beenhanced. In particular, integral provision of the third stage heatexchangers H3 within the pre-catalytic systems 34 can actively controlthe temperature of the pre-catalytic systems 34, and midstream watersupply to the first circular distribution passages 56, the secondcircular distribution passages 47, and the third circular distributionpassages 43 in the vicinity of the pre-catalytic systems 34 can not onlycontrol the temperature of the pre-catalytic systems 34 themselves butcan also appropriately control the temperature of the main catalyticsystems 35 positioned downstream thereof, thereby greatly enhancing theoverall exhaust gas purification performance.

With regard to the heat transfer surface densities (heat transferarea/volume) of the five heat exchangers H1 to H5, that of the firststage heat exchanger H1 is the highest, and the surface densitygradually decreases therefrom toward the fifth stage heat exchangers H5.Furthermore, with regard to the passage cross sectional areas of thefive heat exchangers H1 to H5, that of the first stage heat exchanger H1is the smallest, and the cross sectional area gradually increasestherefrom toward the fifth stage heat exchangers H5. The heat transfersurface densities and the passage cross sectional areas of the firststage to fourth stage heat exchangers H1 to H4 are shown in Table 4.

TABLE 4 Comparison of heat transfer surface density and passage crosssectional area among heat exchangers of different stages Heat transferPassage surface density (m⁻¹) cross sectional area (m²) First stage heat680 0.0008 exchanger Second stage heat 480 0.0009 exchanger Third stageheat 440 0.0009 exchanger Fourth stage heat  90 0.001 exchanger

Gradually decreasing the heat transfer surface density (heat transferarea/volume) from the first stage heat exchanger H1 to the fifth stageheat exchangers H5 minimizes the heat transfer surface density of thefifth stage heat exchangers H5, through which high temperature exhaustgas passes because they are close to the combustion chambers 16, andmaximizes the heat transfer surface density of the first stage heatexchanger H1, through which the exhaust gas whose temperature hasdecreased passes after passing through the exhaust passage 33, therebyaveraging the heat exchange efficiencies across all of the five heatexchangers H1 to H5.

Furthermore, since the exhaust gas coming out of the combustion chambers16 has a high temperature and a large volume, and as a result a highflow rate, maximizing the passage cross sectional area of the fifthstage heat exchangers H5 close to the combustion chambers 16 canminimize the pressure loss. On the other hand, since the exhaust gasthat has decreased in temperature after passing through the exhaustpassage 33 has decreased volume and also a decreased flow rate,minimizing the passage cross sectional area of the first stage heatexchanger H1 can make the evaporator 3 compact.

The effects obtained by setting the heat transfer surface densities andthe passage cross sectional areas of the first stage heat exchanger H1to the fourth stage heat exchangers H4 as shown in Table 3 aresummarized in Table 5.

TABLE 5

It should be noted here that the second stage to fifth stage heatexchangers H2 to H5, which are heat exchangers in the earlier stage asseen from the internal combustion engine 1, are provided for each one ofthe exhaust ports 18, and since the exhaust gases coming from theexhaust ports 18 are not mixed, it is possible to avoid the occurrenceof exhaust interference, thereby preventing any decrease in the outputof the internal combustion engine 1. Furthermore, since there arepressure pulsations in the exhaust gas at the exits of the exhaust ports18, and the exhaust pressure is high, a heat transfer promoting effectcan be expected. FIG. 17 shows a comparison of the heat transferperformance at several Reynolds numbers between a hot air device withoutexhaust pulsations and an internal combustion engine with exhaustpulsations, and it confirms that the internal combustion engine withexhaust pulsations has the higher heat transfer performance. FIG. 18shows a comparison of the heat transfer performance at several Reynoldsnumbers at two different exhaust pressures in a single cylinder internalcombustion engine provided with a grouped pipe type heat exchanger, andit confirms that the higher the exhaust pressure, the higher the heattransfer performance.

In the first stage heat exchanger H1, which is a heat exchanger in thelater stage as seen from the internal combustion engine 1, since theexhaust gases coming from the three exhaust ports 18 are combined into anon-pulsed flow, the exhaust gas can be maintained at a constant hightemperature and, unlike pulsed flow, the exhaust gas can be made to havea steady flow that does not stop, thereby preventing any deteriorationin the heat exchange performance.

Moreover, since the exhaust gas flows from the internal combustionengine 1 side to the exhaust pipe 32 side, whereas water flows from theexhaust pipe 32 side to the internal combustion engine 1 side, theexhaust gas and the water are in a cross-flow state, and the differencein temperature between the exhaust gas and the water can therefore bemaximized across all of the first stage to fifth stage heat exchangersH1 to H5, thereby contributing to an enhancement of the heat exchangeefficiency between the exhaust gas and the water.

Furthermore, as is clear from FIG. 4, the width of the evaporator 3(width of the internal combustion engine 1 in the direction of thecrankshaft) differs little from the width of the three cylinder bores14, and it is extremely compact. Moreover, not only can the evaporator 3be detached from the cylinder head 12 by merely loosening the sixteenbolts 59, thus providing ease of maintenance, but also the entireevaporator 3 is integrated with high rigidity by the cover 71, therebyenhancing the durability against vibration of the internal combustionengine 1.

Furthermore, since the exhaust passage 33 is bent into a three stagezigzag shape and the first stage to fourth stage heat exchangers H1 toH4 are disposed in layers in the radial direction, the overalldimensions of the evaporator 3 can be reduced as much as possible whileminimizing thermal leakage and preventing noise from being dissipatedfrom the interior of the evaporator 3, thereby providing a compactlayout thereof in the cylinder head 12 of the internal combustion engineE.

Moreover, since the first stage to fifth stage heat exchangers H1 to H5are arranged in a labyrinth form by disposing the pre-catalytic systems34 and the main catalytic systems 35 in layers in the radial direction,not only can their silencing effect be effective in preventing exhaustnoise from leaking outside the waste heat recovery system 2, but also anexhaust gas temperature lowering effect can be given, mainly by thefirst stage to fifth stage heat exchangers H1 to H5. This allows anexhaust muffler to be simplified or omitted, thereby making the exhaustsystem itself compact and lightweight. Furthermore, since the decreasein exhaust gas temperature causes the temperature of the exhaust passageto decrease, in particular, on the downstream side of the first stageheat exchanger H1, the degrees of freedom in designing with regard toheat resistance increase, and the use of a material such as a plasticfor the exhaust passage becomes possible. As a result, the degrees offreedom in the shape of the exhaust passage, the degrees of freedom inmounting on a vehicle, the degrees of freedom in terms of coolingcharacteristics, etc. increase, and the degrees of freedom in the designof the entire vehicle, which has been subjected to restrictions byconventional exhaust systems, can be increased, thereby contributing toa reduction in the overall weight of the exhaust system.

Next, the second embodiment of the present invention is explained byreference to FIGS. 19 to 29.

As shown in FIG. 19, an internal combustion engine E includes a cylinderblock 211, a cylinder head 212, and a head cover 213, which arelaminated one on another, and a piston 215 is slidably fitted in acylinder bore 214 formed in the cylinder block 211. Among an intake port217 and an exhaust port 218 individually communicating with a combustionchamber 216 formed in the cylinder head 212, the intake port 217 isbored within the cylinder head 212 as is conventional, but the exhaustport 218 is formed from a separate member and joined to the cylinderhead 212.

The upper end of a stem 221 of an intake valve 220 that opens and closesan intake valve hole 219 abuts against one end of an intake rocker arm223 pivotably supported on an intake rocker arm shaft 222, and the upperend of a stem 226 of an exhaust valve 225 that opens and closes anexhaust valve hole 224 abuts against one end of an exhaust rocker arm228 pivotably supported on an exhaust rocker arm shaft 227. The otherend of the intake rocker arm 223 and the other end of the exhaust rockerarm 228 abut against an intake cam 230 and an exhaust cam 231respectively provided on a camshaft 229 rotating in association with acrankshaft, which is not illustrated, thereby making the intake valve220 and the exhaust valve 225 open and close.

Provided on the side face of the cylinder head 212 on the exhaust sideis an integrated evaporator type exhaust gas purification system C. Thestructure of the integrated evaporator type exhaust gas purificationsystem C is explained by reference to FIGS. 20 to 29.

The evaporator generates vapor having increased temperature and pressureusing the exhaust gas from the internal combustion engine E as a heatsource, and includes an exhaust passage 233 having the exhaust port 218as a base end and extending to an exhaust pipe 232, and heat exchangersH1 to H5 disposed within the exhaust passage 233 and carrying out heatexchange with the exhaust gas; and metal catalytic systems 246A to 246D,which will be described later, are incorporated into the third stageheat exchanger H3.

The exhaust port 218 is formed from a uniform diameter part 218 apositioned on the upstream side of the flow of the exhaust gas, andhaving a substantially constant diameter, and an increasing diameterpart 218 b provided so as to be connected to the downstream side of theuniform diameter part 218 a and having a diameter that increases in atrumpet shape; the fifth stage heat exchanger H5 is provided around theouter periphery of the uniform diameter part 218 a, and the fourth stageheat exchanger H4 is provided within the increasing diameter part 218 b.The fifth stage heat exchanger H5 is formed from about 5 turns of asingle heat transfer tube 234 wound around the outer periphery of theuniform diameter part 218 a. The fourth stage heat exchanger H4 isformed from multiple windings of a single heat transfer tube 235 and ishoused within the increasing diameter part 218 b, and the heat transfertube 234 of the fifth stage heat exchanger H5 runs through an opening(not illustrated) formed in the exhaust port 218 and is connected to theheat transfer tube 235 of the fourth stage heat exchanger H4.

As is clear from reference to FIGS. 27A to 27C, the heat transfer tube235 of the fourth stage heat exchanger H4 is wound in a triple coilshape that is tapered so as to follow the shape of the interior of theincreasing diameter part 218 b of the exhaust port 218; the coil in theinner layer is wound from the rear (the left-hand side in the figure)toward the front (the right-hand side in the figure) while decreasing indiameter and is folded back at the front end; this is followed by thecoil in the middle layer, which is wound from the front toward the rearwhile increasing in diameter and is folded back at the rear end; andthis is followed by the coil in the outer layer, which is wound from therear toward the front while decreasing in diameter. A water inlet shownin FIG. 27B is connected to the third stage heat exchanger H3, which ison the upstream side and will be described later, and a water outletshown in FIG. 27C is connected to the heat transfer tube 234 of thefifth stage heat exchanger H5, which is on the downstream side. Thecircled numerals to shown in FIG. 27A show the route via which waterflows through the heat transfer tube 235.

Winding the heat transfer tube 235 of the fourth stage heat exchanger H4in the triple coil shape that is tapered so as to follow the shape ofthe interior of the increasing diameter part 218 b of the exhaust port218 makes it possible to have a rectifying effect on the exhaust gasthat flows through the increasing diameter part 218 b, therebycontributing to a reduction in the circulation resistance.

As is most clearly shown in FIGS. 20, 21 and 26, a disk-shapeddistribution passage forming member 241 is joined to the rear end of theincreasing diameter part 218 b of the exhaust port 218, and by joininganother disk-shaped distribution passage forming member 242 to the rearface of the distribution passage forming member 241, a second helicaldistribution passage 243 is formed between the two distribution passageforming members 241, 242. The radially outer end of the second helicaldistribution passage 243 is connected to the upstream end of the heattransfer tube 235 of the fourth stage heat exchanger H4. A helicalopening 244 is formed in the two distribution passage forming members241, 242 so as to follow the second helical distribution passage 243.The cross section of the second helical opening 244 is inclined radiallyoutward at the exit side so as to follow the inclination of theincreasing diameter part 218 b of the exhaust port 218, and a largenumber of guide vanes 245 are attached to the interior thereof in aninclined manner. The exhaust gas supplied from the increasing diameterpart 218 b of the exhaust port 218 therefore flows in a spiral whilediffusing radially outward when passing is through the helical opening244.

As is most clearly shown in FIGS. 20, 22 to 24, and 28, the front end ofa cylindrical case 247 covering the outer peripheries of the first stagemetal catalytic system 246A to the fourth stage metal catalytic system246D and the third stage heat exchanger H3 is joined to the distributionpassage forming member 242, a fourth circular distribution passage 250is formed between two annular distribution passage forming members 248,249, which are superimposed one on another and joined to the rear end ofthe cylindrical case 247, and the fourth circular distribution passage250 is connected to the outer end of a first helical distributionpassage 251 formed by curving a pipe in a helical shape. The first stagemetal catalytic system 246A to the fourth stage metal catalytic system246D, which are disposed in line, are each made by formingconcentrically disposed annular corrugated metal supports 252 to 255having four different diameters and supporting an exhaust gaspurification catalyst on the surface thereof. As shown in FIG. 25 in amagnified manner, the phases of the corrugations of the metal supports252 to 255 of each stage of the metal catalytic systems 246A to 246D aredisplaced by half a pitch from each other.

The third stage heat exchanger H3 is formed from four heat transfertubes 256 to 259 that have different diameters and are wound in a coiledshape (see FIG. 28). The four heat transfer tubes 256 and 259 are housedwithin the cylindrical case 247 so that they are concentric with anddisposed alternately with the four metal supports 252 to 255 of thefirst stage metal catalytic system 246A to the fourth stage metalcatalytic system 246D. The downstream ends of the four heat transfertubes 256 to 259 are connected to an intermediate portion of the secondhelical distribution passage 243, and the upstream ends of the four heattransfer tubes 256 to 259 are connected to an intermediate portion ofthe first helical distribution passage 251.

Two cylindrical cases 260, 261 are coaxially disposed radially outsidethe cylindrical case 247 covering the outer peripheries of the firststage metal catalytic system 246A to the fourth stage metal catalyticsystem 246D and the third stage heat exchanger H3, and the second stageheat exchanger H2 is disposed in an annular form between the twocylindrical cases 260, 261. The second stage heat exchanger H2 is formedfrom a large number of heat transfer tubes 262 wound in a coiled shapein one direction and a large number of heat transfer tubes 263 wound ina coiled shape in the other direction, the tubes 262, 263 being disposedalternately so that parts thereof are meshed together, therebyincreasing the placement density of the heat transfer tubes 262, 263within the space. The outer peripheries of the first stage metalcatalytic system 246A to the fourth stage metal catalytic system 246D,and the third stage heat exchanger H3 are thus surrounded by the heattransfer tubes 262, 263 of the second stage heat exchanger H2.

A third circular distribution passage 266 is formed between an annulardistribution passage forming member 264 fixed to the front end of theouter cylindrical case 260 and an annular distribution passage formingmember 265 joined to the front face of the distribution passage formingmember 264. The upstream ends of the heat transfer tubes 262, 263 of thesecond stage heat exchanger H2 are connected to the third circulardistribution passage 266, and the downstream ends of the heat transfertubes 262, 263 are connected to the fourth circular distribution passage250. Fixed to the rear end of the cylindrical case 260 covering theoutside of the second stage heat exchanger H2 is a dish-shaped end cap267 covering the rear faces of the first stage metal catalytic system246A to the fourth stage metal catalytic system 246D and the third stageheat exchanger H3.

A detachable cover 271 forming the outer boundary of the integratedevaporator type exhaust gas purification system C includes aplate-shaped distribution passage forming member 272 having an exhausthole 272 a connected to the exhaust pipe 232 in its center and anannular distribution passage forming member 273 joined to the front faceof the distribution passage forming member 272, and a first circulardistribution passage 274 is formed between the two distribution passageforming members 272, 273. A cylindrical case 275 positioned radiallyoutside and a cylindrical case 276 positioned radially inside extendforward, with a slight gap therebetween, from the distribution passageforming member 273, and a flange 277 provided on the front end of theouter cylindrical case 275 is superimposed on a flange 279 provided onthe rear end of a mounting plate 278 fixed to the distribution passageforming member 242 and they are tightened together to the cylinder head212 by bolts 280.

An annular distribution passage forming member 281 is fixed to the frontend of the inner cylindrical case 276, and a second circulardistribution passage 283 is formed by joining an annular distributionpassage forming member 282 to the front face of the distribution passageforming member 281. The first circular distribution passage 274 and thesecond circular distribution passage 283 have an identical shape andface each other in the rear to front direction. A cup-shaped inner wallmember 284 is housed within the cover 271, and the first stage heatexchanger H1 is disposed between the outer periphery of the inner wallmember 284 and the inner periphery of the inner cylindrical case 276.

The first stage heat exchanger H1 has a similar structure to that of thesecond stage heat exchangers H2; a large number of heat transfer tubes285 wound in a coiled shape in one direction and a large number of heattransfer tubes 286 wound in a coiled shape in the other direction aredisposed alternately so that parts thereof are meshed together, andthese heat transfer tubes 285, 286 surround the outer periphery of thesecond stage heat exchanger H2. The upstream ends of the heat transfertubes 285, 286 are connected to the first circular distribution passage274, and the downstream ends thereof are connected to the secondcircular distribution passage 283.

The materials for the heat transfer tube 234 of the fifth stage heatexchanger H5, the heat transfer tube 235 of the fourth stage heatexchanger H4, the heat transfer tubes 256 to 259 of the third stage heatexchanger H3, the heat transfer tubes 262, 263 of the second stage heatexchanger H2, and the heat transfer tubes 285, 286 of the first stageheat exchanger H1 are preferably heat-resistant stainless steel(austenite type such as SUS 316L or SUS 310S, ferrite type such as SUS430 or SUS 444) or a nickel-based heat-resistant alloy. Joining of theheat transfer tubes is preferably carried out by brazing, laser weldingor mechanical restraint.

Furthermore, with regard to the metal supports 252 to 255 of the firststage metal catalytic system 264A to the fourth stage metal catalyticsystem 246D, heat-resistant stainless steel (e.g., 20% by weight Cr-5%by weight Al ferrite type stainless steel) or a nickel-basedheat-resistant alloy metal foil (thickness 0.1 mm or below) ispreferable.

As is clear from reference to FIG. 29, a water inlet 287, into whichwater that is a source of high pressure vapor is supplied, is providedin the first circular distribution passage 274, which communicates withthe second circular distribution passage 283 via a large number of theheat transfer tubes 285, 286 of the first stage heat exchanger H1, andthe second circular distribution passage 283 communicates with the thirdcircular distribution passage 266 via a communicating passage 288. Thethird circular distribution passage 266 communicates with the fourthcircular distribution passage 250 via the heat transfer tubes 262, 263of the second stage heat exchanger H2, and the fourth circulardistribution passage 250 communicates with four heat transfer tubes 256to 259 of the third stage heat exchanger H3 via the first helicaldistribution passage 251. The four heat transfer tubes 256 to 259 of thethird stage heat exchanger H3 communicate with a vapor outlet 289 viathe second helical distribution passage 243, the heat transfer tube 235of the fourth stage heat exchanger H4, and the heat transfer tube 234 ofthe fifth stage heat exchanger H5.

In this way, while the water that is supplied from the water inlet 287travels to the vapor outlet 289 via the first stage heat exchangerH1→the second stage heat exchanger H2→the third stage heat exchangerH3→the fourth stage heat exchanger H4→the fifth stage heat exchanger H5,it exchanges heat with exhaust gas that comes out of the internalcombustion engine E and flows in a direction opposite to that in whichthe water flows, the water becoming vapor.

That is, while passing through the uniform diameter part 218 a of theexhaust port 218, the exhaust gas coming out of the internal combustionengine E exchanges heat with the fifth stage heat exchanger H5 formedfrom the heat transfer tube 234 wound around the outer periphery of theuniform diameter part 218 a. The exhaust gas that has flowed from theuniform diameter part 218 a of the exhaust port 218 into the increasingdiameter part 218 b exchanges heat by direct contact with the fourthstage heat exchanger H4 formed from the heat transfer tube 235 wound ina triple coil shape and housed within the increasing diameter part 218b. Harmful components are purified from the exhaust gas coming out ofthe exhaust port 218 while passing through the interiors of the firststage metal catalytic system 246A to the fourth stage metal catalyticsystem 246D and, at this point, the exhaust gas exchanges heat with thethird stage heat exchanger H3 formed from the heat transfer tubes 256 to259 arranged concentrically with the first stage to fourth stage metalcatalytic systems 246A to 246D.

The exhaust gas that has passed through the first stage to fourth stagemetal catalytic systems 246A to 246D and the third stage heat exchangerH3 is blocked by the end caps 267 and makes a U-turn, exchanges heatwhile flowing from the rear to the front through the second stage heatexchanger H2 formed from the heat transfer tubes 262, 263 disposedbetween the pair of cylindrical cases 260, 261, then changes directionthrough 180°, exchanges heat while flowing from the front to the rearthrough the first stage heat exchanger H1 formed from the heat transfertubes 285, 286 disposed between the cylindrical case 276 and the innerwall member 284, and is finally discharged into the exhaust pipe 232through the exhaust hole 272 a of the distribution passage formingmember 272.

The exhaust gas that has passed through the second stage heat exchangerH2 diffuses radially outward when passing through the helical opening244 that communicates with the increasing diameter part 218 b of theexhaust port 218, and is given a spiral flow by the guide vanes 245attached to the interior of the helical opening 244. This makes theexhaust gas act uniformly over all of the first stage to fourth stagemetal catalytic systems 246A to 246D and increases the residence time ofthe exhaust gas within the first stage to fourth stage metal catalyticsystems 246A to 246D, thereby enhancing the exhaust gas purificationeffect. As shown in FIG. 25 in a magnified manner, since the phases ofthe corrugations of the metal supports 252 to 255 of each stage of themetal catalytic systems 246A to 246D are displaced by half a pitch fromeach other, a strong turbulent flow can be caused in the exhaust gasflow. This increases the residence time of the exhaust gas within thefirst stage to fourth stage metal catalytic systems 246A to 246D,thereby enhancing the exhaust gas purification effect and the heatexchange efficiency of the adjoining third stage heat exchanger H3.

Furthermore, the flow path lengths of the four heat transfer tubes 256to 259 that include the flow path lengths of parts of the first andsecond helical distribution passages 251 and 243 can be made as uniformas possible by connecting the four heat transfer tubes 256 to 259 of thethird stage heat exchanger H3 to optimal positions on the first helicaldistribution passage 251 and the second helical distribution passage243; that is, connecting opposite ends of the heat transfer tube 256that is radially outside and has a long pipe length to the outside, inthe radial direction, of the first helical distribution passage 251 andthe outside, in the radial direction, of the second helical distributionpassage 243; and connecting opposite ends of the heat transfer tube 259that is radially inside and has a short pipe length to the inside, inthe radial direction, of the first helical distribution passage 251 andthe inside, in the radial direction, of the second helical distributionpassage 243, thereby reducing differences in pressure loss between theheat transfer tubes 256 and 259.

Moreover, since the first stage to fourth stage metal catalytic systems246A to 246D and the third stage heat exchanger H3 are integrated so asto exchange heat with each other, the heat of reaction generated in thefirst stage to fourth stage metal catalytic systems 246A to 246D can berecovered by the third stage heat exchanger H3, thereby enhancing thethermal energy recovery effect and, furthermore, controlling the flowrate of water flowing through the third stage heat exchanger H3 therebyheats and activates the first stage to fourth stage metal catalyticsystems 246A to 246D, or cools the first stage to fourth stage metalcatalytic systems 246A to 246D, thereby enhancing the durability.

In addition, means for controlling the amount of water flowing throughthe third stage heat exchanger H3 may be provided by adding the‘multiple water supply’ structure shown in FIGS. 11, 16, etc. of thefirst embodiment and, more particularly, by reference to FIG. 29,supplying water midstream at four positions in the water supply routefrom the first stage heat exchanger H1 to the fifth stage heatexchangers H5, that is, the third circular distribution passages 266immediately upstream of the second stage heat exchangers H2, the fourthcircular distribution passage 250 or the first helical distributionpassage 251 immediately upstream of the third stage heat exchangers H3,and the second helical distribution passages 243 immediately upstream ofthe fourth stage heat exchangers H4, and individually controlling theamount of water supplied to the second stage to fourth stage heatexchangers H2, H3, H4 according to changes in the operational state (theflow rate of the exhaust gas or the temperature of the exhaust gas) ofthe internal combustion engine 1 and the catalyst temperature (thiswater supply method is called multiple water supply) can yet more finelycontrol the catalyst temperatures of the first stage to fourth stagemetal catalytic systems 246A to 246D at temperatures appropriate to thecatalytic reaction.

The exhaust gas that has passed through the first stage to fourth stagemetal catalytic systems 246A to 246D and the third stage heat exchangerH3 exchanges heat when passing through the first helical distributionpassage 251, which is formed from a helical pipe material. Since thisfirst helical distribution passage 251 diffuses the flow of the exhaustgas, heat spots can be prevented from occurring in the end cap 267 thatis present to the rear of the passage 251 at the position where theexhaust gas turns back; the end cap 267, which is under thermally severeconditions, can be protected; and radiation of heat from the end cap 267can be prevented. Moreover, since the first helical distribution passage251, which is formed from the helical pipe material, has flexibility,differences in thermal expansion between the four heat transfer tubes256 to 259 having different overall lengths can be absorbed.

Furthermore, since the exhaust gas flows from the internal combustionengine E side to the exhaust pipe 232 side, whereas water flows from theexhaust pipe 232 side to the internal combustion engine E side, theexhaust gas and the water are in a cross-flow state, and the differencein temperature between the exhaust gas and the water can therefore bemaximized across all of the first stage to fifth stage heat exchangersH1 to H5, thereby contributing to an enhancement of the heat exchangeefficiency between the exhaust gas and the water. Moreover, since theexhaust passage 233 is bent into a three stage zigzag shape and thefirst stage to third stage heat exchangers H1 to H3 are disposed inlayers in the radial direction, the overall dimensions of the integratedevaporator type exhaust gas purification system C can be reduced as muchas possible while minimizing the thermal leakage and preventing noisefrom being dissipated from the interior thereof, thereby providing acompact layout thereof in the cylinder head 212 of the internalcombustion engine E.

Moreover, since the first stage to third stage heat exchangers H1 to H3and the first stage to fourth stage metal catalytic systems 246A to 246Dare arranged in a labyrinth form by disposing them in layers in theradial direction, not only can their silencing effect be effective inpreventing exhaust noise from leaking outside the integrated evaporatortype exhaust gas purification system C, but also an exhaust gastemperature lowering effect can be given, by mainly the first stage tofifth stage heat exchangers H1 to H5. This allows an exhaust muffler tobe simplified or omitted, thereby making the exhaust system itselfcompact and lightweight. Furthermore, since the decrease in exhaust gastemperature causes the temperature of the exhaust passage to decrease,in particular, on the downstream side of the first stage heat exchangerH1, the degrees of freedom in designing with regard to heat resistanceincrease, and the use of a material such as a plastic for the exhaustpassage becomes possible. As a result, with regard to the internalcombustion engine E for a vehicle, the degrees of freedom in the shapeof the exhaust passage, the degrees of freedom in mounting on thevehicle, the degrees of freedom in terms of cooling characteristics,etc. increase, and the degrees of freedom in the design of the entirevehicle, which has been subjected to restrictions by conventionalexhaust systems, can be increased, thereby contributing to a reductionin the overall weight of the exhaust system.

Although embodiments of the present invention are explained in detailabove, the present invention can be modified in a variety of wayswithout departing from the spirit and scope thereof.

For example, in the first embodiment, the internal combustion engine 1for an automobile is illustrated as the combustion system, but thepresent invention can be applied to any other combustion system.

Industrial Applicability

As hereinbefore described, the combustion gas purification systemrelated to the present invention can be applied to a case in whichharmful components in the combustion gas from an internal combustionengine or any other combustion system are purified by anoxidation/reduction reaction. Furthermore, the internal combustionengine related to the present invention can be applied to one in whichan exhaust gas purification system for purifying an exhaust gas and aheat exchanger for exchanging heat with the exhaust gas are provided inan exhaust passage.

What is claimed is:
 1. A combustion gas purification system wherein acatalytic system that purifies a combustion gas is disposed in anexhaust passage guiding the combustion gas from a combustion system, andat least one part of the catalytic system is provided with temperatureadjustment means for adjusting the temperature thereof, wherein thetemperature adjustment means has a heat transfer tube through which anoperating medium flows and the at least one part of the catalytic systemhas a catalyst support which is placed in direct contact and integratedwith the heat transfer tube of the temperature adjustment means, and theheat transfer tube and the catalyst support are brought into directcontact with the combustion gas at a same position along a flow of thecombustion gas, whereby the temperature adjustment means operates torecover thermal energy of the combustion gas and the operation of thetemperature adjustment means depends on a temperature condition of theoperating medium.
 2. The combustion gas purification system according toclaim 1, wherein the temperature adjustment means is a heat exchanger.3. The combustion gas purification system according to claim 1, whereinthe catalytic system provided with the temperature adjustment means ispositioned on an upstream side of the exhaust passage.
 4. The combustiongas purification system according to claim 1, wherein the temperatureadjustment means also controls the temperature of a part of thecatalytic system other than said one part of the catalytic system. 5.The combustion gas purification system according to claim 1, whereintemperature adjustment means for adjusting the temperature of thecombustion gas is provided in the exhaust passage on an upstream side ofthe catalytic system.
 6. The combustion gas purification systemaccording to claim 5, wherein the temperature adjustment means foradjusting the temperature of the gas is a heat exchanger.
 7. Thecombustion gas purification system according to claim 1, wherein the atleast one part of the catalytic system is formed from a metal.
 8. Thecombustion gas purification system according to claim 1, wherein aplurality of sheets of catalyst support are provided as said catalystsupport and a plurality of heat transfer tubes are provided as said heattransfer tube.
 9. The combustion gas purification system according toclaim 1, wherein the operating medium of the temperature adjustmentmeans flows in a passage and the combustion gas in the exhaust passageflows in a direction substantially opposite to that of a flow of theoperating medium in the passage of the temperature adjustment means. 10.The internal combustion engine according to claim 1, wherein thetemperature adjustment means is constructed to have a passagecross-sectional area that is large on an upstream side of the flow ofcombustion gas near the combustion system and small on a downstreamside.
 11. An internal combustion engine comprising in an exhaustpassage, an exhaust gas purification system that purifies exhaust gasand a heat exchanger that exchanges heat with the exhaust gas, whereinthe heat exchanger has a heat transfer tube through which an operatingmedium flows and at least one part of the exhaust gas purificationsystem has an exhaust gas purifying element support which is placed indirect contact and integrated with the heat transfer tube of at leastone part of the heat exchanger, and the heat transfer tube and theexhaust gas purifying element support are brought into direct contactwith the exhaust gas at a same position along a flow of the exhaust gasso as to be able to exchange heat with each other, whereby the heatexchanger operates to recover thermal energy of the exhaust gas and theoperation of the heat exchanger depends on a temperature condition ofthe operating medium.
 12. The internal combustion engine according toclaim 11, wherein stirring means for stirring the flow of the exhaustgas is provided on an upstream side of the section where the exhaust gaspurification system and the heat exchanger are in contact.
 13. Theinternal combustion engine according to claim 11, wherein the at leastone part of the exhaust gas purification system is formed from a metal.14. The internal combustion engine according to claim 11, wherein aplurality of corrugated metal supports are provided as said catalystsupport and a plurality of heat transfer tubes are proved as said heattransfer tube.
 15. The internal combustion engine according to claim 14,wherein the plurality of heat transfer tubes are concentric with anddisposed alternately with the plurality of metal supports at a contactsite.
 16. The internal combustion engine according to claim 11, whereinthe exhaust gas in the exhaust passage flows in a directionsubstantially opposite to that of a flow of the operating medium in theheat exchanger.
 17. The internal combustion engine according to claim11, wherein the heat exchanger is constructed to have a passagecross-sectional area that is large on an upstream side of the flow ofthe exhaust gas near a combustion chamber and small on a downstreamside.
 18. A combustion gas purification system wherein a catalyticsystem that purifies a combustion gas is disposed in an exhaust passageguiding the combustion gas from a combustion system, and at least onepart of the catalytic system is provided with temperature adjustmentmeans for adjusting the temperature thereof, wherein the temperatureadjustment means uses an operating medium and the at least one part ofthe catalytic system is integrated with, the temperature adjustmentmeans so that components of the temperature adjustment means surroundcomponents of the at least one part of the catalytic system at a contactsite, whereby the temperature adjustment means operates to recoverthermal energy of the combustion gas and the operation of thetemperature adjustment mean depends on a temperature condition of theoperating medium, wherein the components of the at least one catalyticsystem include a plurality of sheets of catalyst support and thecomponents of the temperature adjustment means include a plurality ofheat transfer tubes; and wherein the plurality of heat transfer tubesare formed in a zigzag shape and are interlaced with the plurality ofsheets of catalyst support at the contact site.